The present invention relates to a developing device of the type feeding a one-ingredient or two-ingredient type developer, forming a thin toner layer on a developing roller or toner support member and developing a latent image with the toner layer, and a printer, facsimile apparatus, copier or similar image forming apparatus including the same.
Developing devices of the type described and featuring unique toner supporting systems are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 56-40862, 59-151173 and 8-254933. The developing device taught in Laid-Open Publication No. 56-40862 includes a developing roller for supporting toner contained in a two-ingredient type developer. An oscillating electric field is formed between the developing roller and a photoconductive element spaced therefrom for developing a latent image formed on the element. This type of development is generally referred to as non-contact development.
The developing device disclosed in the above Laid-Open Publication No. 59-151173 is similar to the developing device disclosed in Laid-Open Publication No. 56-40862 except that the developing roller includes toner collecting means. The toner collecting means, however, increases the number of parts, unit capacity, and cost.
The developing device proposed in Laid-Open Publication No. 8-254933 includes lubricant applying means for applying a lubricant to a photoconductive element. Toner concentration sensing means is responsive to the concentration of toner deposited on the photoconductive element outside of an image area. Control means controls the lubricant applying means in accordance with the output of the toner concentration sensing means.
On the other hand, in a contact development type of developing device, a developing roller is held in contact with a photoconductive element with the intermediary of a toner layer. Toner is charged by friction acting between it and the developing roller. Assume that the toner is chargeable to negative polarity. Then, if the surface layer of the developing roller is charged to the same polarity as the toner, the toner has its charge noticeably lowered or is charged to the opposite polarity. As a result, the toner fails to sufficiently develop a latent image and contaminates the background of the photoconductive element, thereby degrading image quality to a critical degree.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 4-372981, 5-46009, 5-210292, 6-161226, 2000-19835 and 2000-39763.
It is therefore an object of the present invention to provide a developing device capable of preventing a toner support member from charging toner by friction to thereby surely develop a latent image. In accordance with the present invention, in an image forming apparatus for feeding either a one-ingredient type or a two-ingredient type developer and causing only toner to selectively deposit on a toner support member to thereby develop a latent image formed on a photoconductive element, the toner support member has at least a surface layer thereof formed of a material chargeable to the same polarity as the toner. At least the surface layer of the toner support member may contains a fluorine-containing substance.